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Jang, Seongwan,Kim, A Young,Seo, Won Seok,Park, Kang Hyun Springer US 2015 NANOSCALE RESEARCH LETTERS Vol.10 No.1
<P>Phosphomolybdic acid (PMA, H<SUB>3</SUB>PMo<SUB>12</SUB>O<SUB>40</SUB>) functioned as a catalyst for reactions of secondary propargylic alcohols and nucleophiles. Highly stable and magnetically recyclable mesoporous silica spheres (MMS) embedded with FeCo-graphitic carbon shell nanocrystals (FeCo/GC@MSS) were fabricated by a modified Stöber process and chemical vapor deposition (CVD) method. The FeCo/GC@MSS were loaded with phosphomolybdic acid (PMA@FeCo/GC@MSS), and their catalytic activity was investigated. Propargylic reactions of 1,3-diphenyl-2-propyn-1-ol with a wide range of nucleophiles bearing activating substituents were catalyzed under mild conditions. It was found that the MMS possess mesoporosities and have enough inner space to load FeCo and phosphomolybdic acid. The FeCo/GC@MSS were found to be chemically stable against acid etching and oxidation. This suggests that the nanocrystals can be used as a support for an acid catalyst. Moreover, the magnetic property of the nanocrystals enabled the facile separation of catalysts from the products.</P>
Study on mechanical properties of kaolin-based geopolymer with various Si/Al ratio and aging time
Gao Binghuan,Jang Seongwan,Son Hyeonjin,Lee Hee Jung,Lee Hwan Jong,Yang Jeong Jik,Bae Chang-jun 한국세라믹학회 2020 한국세라믹학회지 Vol.57 No.6
Geopolymers are a class of aluminosilicate-based ceramics that contain 3D network synthesized by condensation of tetrahedral aluminosilicate units, produced by the aluminosilicate raw materials and alkaline activators. The Si/Al ratio and aging time are the crucial parameters which infl uence the reaction degree of geopolymerization process and the reaction time, aff ecting the fi nal properties, respectively. Here, we investigated the eff ect of Si/Al ratio and aging time on the microstructure and mechanical properties of kaolin-based geopolymers, where SEM, XRD, and piston on three ball test were applied at the diff erent Si/Al ratio and the aging time. Given the higher ratio of Si/Al and longer aging time, geopolymer-based matrix was densifi ed and high crystalline phases were evolved. Furthermore, the highest fl exural strength of specimen, with the Si/ Al ratio of 2.49 and aging time of 1 day, was 19.5 MPa.
Lee, Yohan,Jang, Seongwan,Cho, Chang-Woo,Bae, Jong-Seong,Park, Sungkyun,Park, Kang Hyun American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.11
<P>In this work, rhodium nanoparticles were synthesized using hydrothermal method that is simple and easy to manipulate reaction and use nontoxic supercritical water. The rhodium nanoparticles were formed in uniform size and shape. These Rh NPs also acted as a efficient heterogenous catalyst in reduction of 4-nitrophenol to 4-aminophenol. Moreover, the rhodium nanoparticles can be recycled without any loss in catalytic activity, and showed highly catalytic activity for various nitroarenes. Therefore, this method will contribute greatly to the development of environmental field and be suitable for use in the industry.</P>
Dermal Toxicity of Flake-Like 관-Alumina Pigments.
Kwon, TaeWoo,Seo, HyunJeong,Jang, Seongwan,Lee, Sang-Geun,Park, Sungkyun,Park, Kang Hyun,Youn, BuHyun American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.2
<P>Aluminum is one of the most widely used nonferrous metals and an important industrial material, especially for automotive coatings. However, potential toxicity caused by aluminum in humans limits the used of this metal. 관-alumina is the most stable form of aluminum in various phases. Although the results of studies evaluating the dermal toxicity of 관-alumina remained unclear, this compound can still be used as a pigment in cosmetics for humans. In the current study, we further evaluated the dermal cytotoxic effects of 관-alumina on human skin cells and an in vivo mouse model. We also measured the in vitro penetration profile of flake-like 관-alumina in porcine skin and assessed the degree of cellular metabolic disorders. Our findings demonstrated that treatment with flake-like 관-alumina did not significantly affect cell viability up to 24 h. This compound was found to have a non-penetration profile based on a Franz modified diffusion cell assay. In addition, flake-like 관-alumina was not found to induce dermal inflammation as assessed by histology of epidermal architecture, hyperplasia, and the expression of Interleukin-1관 and Cyclooxygenase-2. Results of the cellular metabolic disorder assay indicated that flake-like 관-alumina does not exert a direct effect on human skin cells. Taken together, our findings provided not only evidence that flake-like 관-alumina may serve as a pearlescent pigment in cosmetics but also experimental basis utilizing 관-alumina for human application. Our results also obviously provide new insight of the further toxicity study to aluminum based nanoparticles for skin.</P>
사형 주조 3D 프린팅용 소재의 기계적 특성 및 신뢰성
손현진,장성완,이환종,양정직,정영근,배창준,Son, Hyeon Jin,Jang, Seongwan,Lee, Hwan Jong,Yang, Jeong Jik,Jeong, Yeong Geun,Bae, Chang-Jun 한국재료학회 2020 한국재료학회지 Vol.30 No.1
Sand casting 3D printing uses a binder jetting method to produce a mold having complicated shape by spraying a binder on sand coated with activator. Appropriate heat treatment process in sand mold fabrication can increase the degree of polymerization to improve flexural strength. However, long heat treatment of over 24 hours decreases flexural strength and reliability due to chemical bond decomposition through thermal degradation. The main role of the activator is to control the reaction rate between the polymer chains. As a result, when the activator composition is increased from 0.15 wt% to 0.25 wt%, the flexural strength is increased by 218 N/㎠. However, excess activator (0.40 wt%) has been shown to decrease reliability without increasing flexural strength. The main role of the binder is to control the flexural strength of the specimen. As the binder composition is increased from 2.00 wt% to 4.00 wt%, the flexural strength increases to about 255 N/㎠, indicating the maximum flexural strength increase. Finally, the reliability of the flexural strength of the fabricated specimens is evaluated by a Weibull plot. Weibull modulus calculations are used to evaluate the flexural strength reliability of the specimens, and maximum reliability value of 11.7 is obtained at 0.20 wt% activator composition. Therefore, it is confirmed that this composition has maximum flexural strength reliability.